Bambusuril as a One-Electron Donor for Photoinduced Electron Transfer to Methyl Viologen in Mixed Crystals

Methyl viologen hexafluorophosphate
(MV2+·2PF6–) and dodecamethylbambus[6]­uril
(BU6) form
crystals in which the layers of viologen dications alternate with
those of a 1:2 supramolecular complex of BU6 and PF6–. This arrangement allows for a one-electron reduction
of MV2+ ions upon UV irradiation to form MV+• radical cations within the crystal structure with half-lives of
several hours in air. The mechanism of this photoinduced electron
transfer in the solid state and the origin of the long-lived charge-separated
state were studied by steady-state and transient spectroscopies, cyclic
voltammetry, and electron paramagnetic resonance spectroscopy. Our
experiments are supported by quantum-chemical calculations showing
that BU6 acts as a reductant. In addition, analogous photochemical
behavior is also demonstrated on other MV2+/BU6 crystals
containing either BF4– or Br– counterions.